If a counterweight is stuck in a lift shaft, or travels onto the buffer arranged in the lift shaft pit, the support means or cable at the counterweight side becomes loose or slack. The traction of the support means on the drive pulley can, however, nevertheless be sufficient for the drive unit to be able to raise an empty or only lightly-loaded lift cage. According to European Norm EN 81-1, paragraph 9.3 c), it should not be possible to raise an empty lift cage when a counterweight rests on the buffer. Through raising of the lift cage dangerous situations could arise in which the traction between the support means and drive pulley is no longer sufficient and the lift cage would then drop back or crash. In the opposite running direction, raising of the counterweight is also not desired.
The risk of raising the lift cage or the counterweight exists, particularly when belts or synthetic fibre cables serve as support means with grippy running surfaces.
A hoisting cable monitoring means has become known from the specification in DD 290 399 A5 in which the hoisting cable is led through an eye-shaped contact frame. If the cable is loose or slack an electric switching-off of the drive is carried out by means of the contact frame. Such a construction, however, is not feasible in all lifts.
It is accordingly a purpose of the present invention to provide a simplified mechanism for modernizing a lift installation and providing a monitoring capability. A drive unit may be easily exchanged for a drive of the present invention. In addition, a safety device for monitoring the support means for slackness or unallowed raising of the lift cage or the counterweight can be installed at the same time.